Piezoelectric ceramics is used widely for piezoelectric ceramic devices, such as piezoelectric resonators, piezoelectric filters, piezoelectric actuators, piezoelectric transformers, and piezoelectric buzzers. Multi-layered piezoelectric devices have been developed according to recent demand to have reduced size and thickness and to have high performance
Conventional piezoelectric compositions are sintered at high sintering temperatures of about 1,200° C. The temperatures have the multi-layered piezoelectric devices include expensive platinum or palladium as material of internal electrodes, thus increasing production cost of the devices.
To decrease the sintering temperature of the ceramics, Japanese Patent Laid-Open Publication No.9-169566 discloses that the sintering temperature is reduced by adding Cu and W to composition essentially consisting of a perovskite-structure multiple oxide containing Pb, Zr, and Ti. The temperature allows relatively inexpensive silver-palladium alloys to be used as material of the internal electrodes of the piezoelectric devices.
To further reduce the sintering temperature and the content of palladium, Japanese Patent Laid-Open Publication No.10-7458 discloses that CoO and PbO are added to composition essentially consisting of PbTiO3, PbZrO3, Pb(Mn1/3Nb2/3) and Pb(Co1/3Nb2/3).
The piezoelectric ceramic composition disclosed in Japanese Patent Laid-Open Publication No.9-169566 is sintered at a sintering temperature of about 1,100° C. and has piezoelectric characteristics, e.g. a coupling coefficient Kp ranging about from 0.50 to 0.57.
The piezoelectric ceramic composition disclosed in Japanese Patent Laid-Open Publication No.10-7458 is sintered at a sintering temperature of about 900° C. and has piezoelectric characteristics, e.g. a coupling coefficient Kp ranging about from 0.30 to 0.50, and a Curie temperature, which indicates heat resistance, ranging about from 200° C. to 300° C.
As above, there has not been composition that has a sintering temperature of about 900° C., piezoelectric characteristics, e.g. a coupling coefficient Kp of at least 0.50, and a Curie temperature of at least 300° C. among the conventional ceramic compositions. The conventional compositions allow relatively inexpensive silver-palladium alloys to be used as the material of the internal electrodes, however, has poor characteristics as piezoelectric ceramics.